Lung cancer remains the most common cause of cancer death in the US with over 150,000 deaths per year. Radiation therapy (RT) is the main curative modality for inoperable non-small cell lung cancer (NSCLC). This study addresses the poor local control rates of conventional RT, where treatment success is constrained by: 1. Limits on radiation doses due to radiation pneumonitis, and for patients receiving concurrent chemotherapy(ChT), esophagitis. 2. Respiration-induced tumor motion, requiring larger treatment fields and increased treatment toxicity. 3. Uncertainties in tumor definition due to limited sensitivity and accuracy of CT imaging. 4. Uncertainties in RT treatment delivery and inability to confirm daily treatment accuracy. Previous studies have demonstrated the advantages of 3-D Conformal RT (3DCRT) and deep inspiration breath hold for reducing treatment uncertainties and normal tissue toxicities. In this proposal, significantly advanced technologies will be joined in an integrated approach to RT of NSCLC. These new strategies are: 1. Inverse Treatment Planning and Intensity Modulated RT for improved conformal normal tissue avoidance. 2. Respiratory Gating to control breathing motion during imaging, simulation, and treatment. 3. Improved tumor detection and delineation by combining FDG-PET and CT imaging. 4. Improved treatment verification using electronic portal imaging and megavoltage cone beam imaging. These new technologies will provide unprecedented accuracy in identifying and targeting tumors, and in minimizing normal tissue toxicity, thus permitting higher treatment doses. Our proposed clinical study targets 3 groups of surgically unresectable patients for escalation to the following maximum doses: (1) 99Gy to 'small' tumors; (2) 90Gy to 'large' tumors for patients ineligible for ChT, or who have previously received ChT; (3) 80 Gy RT for patients receiving concurrent ChT. We hypothesis that this high technology approach will permit treatment to higher doses without increasing normal tissue toxicity, and improve local control.